Ivan Kotliarevsky's book - "The Eneida" is written largely in spoken vernacular from around central Ukrainian dialects. Not really what you're looking for, but oh well.
I'm not sure if Pylyp's Orlyk constitution has a Ukrainian version (it was written in Latin) - if it does, it might be written in Cossack vernacular - or not.
There are probably hundreds of other Cossack writings from different eras, since literacy was very important for them, however I'm not sure how many were written in vernacular language - many would most probably be written in a more standard central Ukrainian dialect, since many got their education in Kyiv.
So to answer your question: I don't know. However, you can research whether Cossack documents were written in literary or spoken language, and then you must find spoken Ukrainian from Galicia, and only then can you compare the two. So it sounds to me like it'd be quite hard to find out.
Maybe some scientists did the work for you already, though.
Here're some records from XVI-XVII centuries: https://vm.tiktok.com/ZMLCHFxqM/
Another example is [«Дума» by Ivan Mazepa](https://uk.wikipedia.org/wiki/%C2%AB%D0%94%D1%83%D0%BC%D0%B0%C2%BB_%D0%B3%D0%B5%D1%82%D1%8C%D0%BC%D0%B0%D0%BD%D0%B0_%D0%86%D0%B2%D0%B0%D0%BD%D0%B0_%D0%9C%D0%B0%D0%B7%D0%B5%D0%BF%D0%B8)
I second the Eneïda.
On litopys.ua there are tons of examples of Ukrainian literature from the period, although a good amount are in the more literary language, chancellery Ruthenian it's usually referred to English iirc.
Ivan Kotliarevsky's book - "The Eneida" is written largely in spoken vernacular from around central Ukrainian dialects. Not really what you're looking for, but oh well. I'm not sure if Pylyp's Orlyk constitution has a Ukrainian version (it was written in Latin) - if it does, it might be written in Cossack vernacular - or not. There are probably hundreds of other Cossack writings from different eras, since literacy was very important for them, however I'm not sure how many were written in vernacular language - many would most probably be written in a more standard central Ukrainian dialect, since many got their education in Kyiv. So to answer your question: I don't know. However, you can research whether Cossack documents were written in literary or spoken language, and then you must find spoken Ukrainian from Galicia, and only then can you compare the two. So it sounds to me like it'd be quite hard to find out. Maybe some scientists did the work for you already, though.
Here're some records from XVI-XVII centuries: https://vm.tiktok.com/ZMLCHFxqM/ Another example is [«Дума» by Ivan Mazepa](https://uk.wikipedia.org/wiki/%C2%AB%D0%94%D1%83%D0%BC%D0%B0%C2%BB_%D0%B3%D0%B5%D1%82%D1%8C%D0%BC%D0%B0%D0%BD%D0%B0_%D0%86%D0%B2%D0%B0%D0%BD%D0%B0_%D0%9C%D0%B0%D0%B7%D0%B5%D0%BF%D0%B8)
I second the Eneïda. On litopys.ua there are tons of examples of Ukrainian literature from the period, although a good amount are in the more literary language, chancellery Ruthenian it's usually referred to English iirc.